Method of manufacturing laminated stator with improved flux pattern

ABSTRACT

A stator for a fractional horsepower motor has a mounting hole of reduced dimensions for fixing the position of motor mounting brackets which support a rotor. The configuration of the mounting holes increase the area where magnetic flux may pass. One configuration reduces the depth of the mounting hole to one or two laminates of each side of the stator. Another configuration is an elongated hole which lies in the direction of the magnetic flux. Each laminate may have a tang which interlocks with tangs on other laminates when the laminated stack is squeezed together in a punch press.

This application is a division, of prior application Ser. No. 07/870,274filed Apr. 17, 1992, now U.S. Pat. No. 5,248,911.

This invention relates to fractional horsepower electric motors and moreparticularly to stators having much greater operating efficiencyespecially--but not exclusively--for use in such motors.

Fractional horsepower motors are used in small appliances, toys, andother similar devices, which is a business field where cost is extremelyimportant. Even the smallest savings may spell a difference betweencommercial success and failure. Also, the efficiency of the motor isimportant since most manufacturers of such appliances, toys, and thelike wish to use the smallest motor which can reliably perform itsfunction.

One of the factors which affects the efficiency of electric motors isthe ability of the iron laminations used in the stator to carry magneticflux.

It is normal to mount the brackets which hold the motor bearingsdirectly upon the stator in order that the relationship between thestator bore and the bearing, and thus the rotor, can be closelycontrolled. This close control results in a more uniform and possiblysmaller air-gap which enhances the performance of the motor.

The brackets are usually constructed with a protuberance, or boss,surrounding the hole through which the securing bolt or rivet isinserted. Since the size of the boss must be such as to contain not onlythe bolt or rivet, but also sufficient to contain bracket material toprovide strength, it becomes necessary to make the mounting holes in thelamination larger than is required to merely clear the bolt or rivet. Ina typical stator, the holes provided for mounting are 0.375-inch indiameter but contain a bolt with a diameter of only 0.164-inch.

The need to use such a relatively large hole through the stator mayoften cause the iron adjacent to these holes to become saturated withmagnetic flux, thereby reducing the efficiency of the motor.

Since laminations are produced on progressive dies, it has beennecessary to make the clearance holes in all laminations of this largediameter, even though the boss on the mounting bracket is engaged onlywith a small number of laminations on either end of the stator.

There is a need to make the mounting holes large enough to receive theparts inserted into them. If the stator is an inch thick, for example,it may mean that forty laminate pieces must be almost perfectly aligned.It has heretofore been too expensive to make some laminates with largeholes and some with small holes because, during assembly, the two sizesof laminates had to be sorted and assembled in a proper order.Therefore, all forty laminates have had large holes.

There are two approaches to a solution of these and similar problems.First, one might reduce the need for oversize holes by a redesign of theparts which must fit into the holes. Second, there may be a more precisemethod of assembling the laminate plates when the stator is manufacturedso that some laminates may be different from other laminates.

Accordingly, an object of this invention is to improve the efficiency offractional horsepower motors without substantially increasing the costthereof.

An object of this invention is to provide a means whereby the bracketsmay be securely and accurately located without the need to remove anymore magnetic material than is needed to clear only the bolt.

Another object of this invention is to provide a more efficientdistribution of magnetic flux in the stator of fractional horsepowermotors.

Yet another object of the invention is to produce superior statorsespecially--although not exclusively--for fractional horsepower motors.

In keeping with an aspect of this invention, these and other objects areaccomplished by providing a way of reducing the disruptive effect uponmagnetic flux distribution which occurs as a result of large mountingholes in laminates of a stator. In one embodiment, the shape of theholes are changed to a configuration which has a minimum effect upon theflux distribution.

The preferred embodiments of the invention are shown in the attacheddrawings, wherein:

FIG. 1 is an exploded view, in perspective of a fractional horsepower

FIG. 2 illustrates flux distribution problems which have beenencountered as a result of large mounting holes used in the prior artmodes of the type shown in FIG. 1;

FIG. 3 shows a fragment of a motor bracket used in the prior art withthe large holes of FIG. 2;

FIG. 4 schematically shows a manufacturing technique for assemblingstator plates, which may be used to produce superior stators which mayhave smaller holes;

FIG. 5 is a cross section of a stator showing a fragment of an exemplaryfour laminate plates incorporating the invention;

FIG. 6 schematically illustrates a way of providing mounting holes in astator with less disruption of the flux pattern in the stator; and

FIG. 7 is a fragment of a motor bracket (similar to the fragment of FIG.3) for use with the stator holes of FIG. 6.

A fractional horsepower motor (FIG. 1) has a laminated magnetic stator20 with a coil assembly 22 mounted thereon. An exemplary seven laminatesL1-L7 are here shown; however many more are usually provided, such asforty laminate plates in a stator which is one inch thick. A relativelylarge bore 24 extends through the stator to receive a rotor 26. Therotor 26 should be centered in bore 24 so that there is a uniform airgap surrounding it. Therefore, two motor bearing brackets 28, 30 arebolted on to opposite sides of the stator.

Each of these motor bearing brackets has a bearing 31 for receiving anend of shaft 32, 32 on rotor 26. The brackets are elongated memberswhich include protrusions 34, 36 on opposite arms 38, 40 of thebrackets. The protrusions fit into mounting holes 42, 44 which areoppositely disposed on either side of bore 24. The positions of themounting holes 42, 44, relative to the location of bore 24, insure thatthe rotor 26 is properly positioned within bore with a proper air gap.

In order to mount the brackets 28, 30, the holes 42, 44 are maderelatively large (0.375-inch diameter, in one example) to receive theprotrusions 34, 36. Since brackets 28, 30 are usually made of aluminumor zinc, which does not carry magnetic flux, the protrusions do nothingfor the flux problems. The large diameter of holes 42, 44 is requiredfor mechanical strength since the protrusions 34, 36 must contain holes54, 56 which are large enough to receive bolts 46 48 (0.164-inchdiameter in the noted example). The bolts, which pass through holes50-56 are made of steel and therefore do carry some flux; however, thebeneficial effect of these bolts is minimal because they have a verysmall diameter compared to the holes 42, 44. Therefore, the flux F1tends to be concentrated in areas A1, A2 of the stator 20 which are onopposite sides of the mounting holes 42, 44. This makes the statorsrelatively inefficient and might even cause a magnetic saturation of thestator which could cause the motor to fail.

According to the invention, more magnetic material is retained in thestator by either of two techniques, or by a combination of the twotechniques.

A first technique is to construct the stator in a manner which insuressubstantially perfect assembly and alignment of the laminates and of theholes 42, 44. The laminates are made in a progressive die which producesan upstanding tang 58, 60, 62 (FIG. 4) on each laminate L1, L2, L3 . . .As each laminate completes its trip through the progressive die, itdrops into an alignment chute. A counter counts the laminates as theyenter the chute. When a predetermined number of the laminates areaccumulated in the chute, the punch press exerts enough pressure uponthem to cause the tangs 58-62 to interlock and clinch together in amanner which holds all laminates securely in place. The interlockingtangs tend to hold the laminates tighter and more predictably.

The exact number of laminates present and the locations of theindividual laminates are known so that the outside two or threelaminates on each side of the stator may be made in a different waywithout simultaneously creating an assembly problem requiring a sortingof the laminates.

As a result of the assembly of laminates within the chute, it ispossible to have larger diameter holes in a selected number of laminateson each side of the stator and small diameter holes in the laminates atthe center of the stator. Thus the previous need for large diameterholes extending entirely through the stator and the attendant loss ofmagnetic material is eliminated. With the described constructed andclinched laminate stator, the holes for receiving the protrusions may bemade much more shallow. For example, as shown in FIG. 5 the large hole64 only appears in the first two laminates L1, L2. The protrusion 66 hasa length H which is substantially equal to the depth D of the hole 64.The remainder of the holes 68 in the laminates are only large enough toreceive the bolt 70 which holds the assembly together. Thus, all of thelaminates, except for the two outside laminates on either side, maycarry more flux.

In order to make the laminates shown in FIG. 5, a progressive die firstpunches the small diameter holes 68 in each and every laminate. Acounter counts to determine (1) how many laminates to clinch togetherand (2) which laminates require the larger hole 64. For example, if astator has forty laminates, the counter causes the small hole 68 to beover punched to become a large hole 64 in the first, second,thirty-ninth and fortieth laminates. This over-punching is accomplishedby a punch which is known as a "gagging" punch. The laminates numberedthree through thirty-eight retain large amounts of flux carrying metalin the areas A1, A2, FIG. 2.

The solution of FIGS. 4, 5, requires the use of special dies for makingthe laminates, which is fine if the company making the motor has thenecessary machine tools. However, many companies purchase the laminatesfrom outside vendors who would not want to have special tools, dies andprocedures for a single customer, who might want many differentcombinations of laminates for different sized motors.

Therefore, for this condition where all laminates should be identical,the embodiment of FIGS. 6, 7 may be used. Here, the shape of the holes72, 74 are changed to have the diameter of a small bolt hole with keyslots 76, 78 extending from opposite sides. The key slots 76, 78 lie inalignment with the direction of magnetic flux F2, as shown in FIG. 6.Since the key slots are relatively narrow in this direction of flux,they have only a negligible effect upon the total flux and do not causean appreciable concentration of flux in the areas A3, A4, such as theconcentration shown at A1, A2 in FIG. 2.

The motor bracket 80 (FIG. 7) for this embodiment has a relatively smallprotrusion 82, but it derives sufficient mechanical strength fromoppositely disposed keys 84, 86 to enable it to serve its function.

A combination of the techniques of FIGS. 4-7 would lead to a hole in theshape 72-78 (FIG. 6) limited to two or three laminations on oppositesides of the stator.

Those who are skilled in the art will readily perceive how to modify theinvention. Therefore, the appended claims are to be construed to coverall equivalent structures which fall within the true scope and spirit ofthe invention.

The claimed invention is:
 1. A method of manufacturing laminatedstators, especially for fractional horsepower motors, said methodcomprising the steps of:(a) stamping said laminates on a punch press,each of said laminates having a configuration which clinches themtogether when a stack of laminates are pressed together; (b) countingsaid laminates as they are produced, (c) altering the configuration ofselected laminates in said stack in order to have large diameter bracketmounting holes on opposite sides of said stack of laminates and smalldiameter screw receiving holes in the remainder of said laminates; (d)assembling a counted number of said laminates into said stack as theyare produced; and pressing the counted assembly of step (d) to clinchthem together.
 2. The method of claim 1 wherein step (a) comprises thefurther step of forming said laminates with upstanding tangs which nesttogether as they are assembled in step (d) and clinch together as theyare pressed in step (e).
 3. The method of claim 1 wherein the alteringof step (c) comprises the further step of forming large mounting bracketreceiving holes on a limited number of laminates on the opposite sidesof said stator.
 4. A method of manufacturing laminated statorscomprising the steps of:(a) forming a plurality of identical statorlaminates, each of said laminates having at least one relatively smalldiameter bolt hole formed therein, said small diameter hole beinglocated at a place in said stator which improves magnetic fluxdistribution in said laminate; (b) identifying at least one of saidlaminates which will be assembled on an outside of a stack of laminates;and (c) over punching said small diameter bolt hole in said onelaminate, said over punching making a larger diameter hole whichfacilitates an assembly of a motor using said laminate, withoutsimultaneously increasing the diameter of the remainder of the boltholes or disturbing said improved flux distribution in the remainder ofsaid laminates.
 5. The method of claim 4 wherein step (a) comprisesforming in each laminate two key slots extending from opposite sides ofsaid small diameter bolt holes, said key slots being aligned with fluxlines in said laminate in order to provide said improved flux lines. 6.The method of claim 5 and the added step of accumulating a predeterminednumber of said laminates as they are formed, whereby a batch oflaminates are assembled to form a completed stator, said one laminatebeing on an outside of said batch of laminates.
 7. The method of claim 6wherein step (b) includes the added step of submitting at least thefirst and last laminate in said accumulated batch for said over punchingin step (c) whereby the outside laminates on both sides of said statormay receive in said over punched hole a member which has a diameter thatis larger than the diameter of a bolt which may pass through said boltholes.
 8. The method of claim 6 wherein step (b) includes the added stepof submitting at least the first two and last two laminates in saidaccumulated batch for said over punching in step (c) whereby the twooutside laminates on each side of said stator may receive a member whichhas a diameter that is larger than the diameter of a bolt which may passthrough said bolt holes.
 9. The method of claim 6 wherein there is achute into which said laminates are directed as they are formed in orderto accumulate said batch of laminates and the added step of overpunching at least the first and the last laminates directed into saidchute at the start and the end of said accumulation of each batch ofsaid stator.
 10. A method of manufacturing laminated stators, especiallyfor fractional horsepower motors, said method comprising the steps of:a)stamping said laminates on a punch press, said stamped laminates havingsmall bolt holes; b) counting said laminates as they are produced inorder to accumulate a batch of said laminates; c) altering theconfiguration of selected laminates in said batch in order to providelarge diameter bracket mounting holes on opposite sides of a statorconstructed from said laminate and small diameter bolt holes remainingin the rest of said laminates; and d) assembling said counted number ofsaid laminates into said stator as they are produced.
 11. The method ofclaim 10 wherein step (a) includes the further step of forming each ofsaid laminates with a configuration which clinches them together whensaid batch of laminates are pressed together; and the added step ofpressing together the batch of counted laminates which are accumulatedin step (c) in order to clinch them together, there being at least twoof said selected laminates with said large diameter holes on each sideof said pressed together laminates.
 12. The method of claim 11 whereinsaid configuration of said laminates comprises forming upstanding tangswhich nest together as they are assembled in step (d), said upstandingtangs clinching together as they are pressed together in the added step.